vim-patch:8.2.1852: map() returing zero for NULL list is unexpected

Problem:    map() returing zero for NULL list is unexpected.
Solution:   Return the empty list. (closes vim/vim#7133)

https://github.com/vim/vim/commit/ffdf8adfa8108d4765fdc68abbd2fe49a4292b25

Co-authored-by: Bram Moolenaar <Bram@vim.org>

4 files changed, 12 insertions, 9 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index ffbe66aa25..8bd91ec9a2 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -4786,20 +4786,20 @@ void filter_map(typval_T *argvars, typval_T *rettv, int map)
   int save_did_emsg;
   int idx = 0;
 
+  // Always return the first argument, also on failure.
+  tv_copy(&argvars[0], rettv);
+
   if (argvars[0].v_type == VAR_BLOB) {
-    tv_copy(&argvars[0], rettv);
     if ((b = argvars[0].vval.v_blob) == NULL) {
       return;
     }
   } else if (argvars[0].v_type == VAR_LIST) {
-    tv_copy(&argvars[0], rettv);
     if ((l = argvars[0].vval.v_list) == NULL
         || (!map
             && var_check_lock(tv_list_locked(l), arg_errmsg, TV_TRANSLATE))) {
       return;
     }
   } else if (argvars[0].v_type == VAR_DICT) {
-    tv_copy(&argvars[0], rettv);
     if ((d = argvars[0].vval.v_dict) == NULL
         || (!map && var_check_lock(d->dv_lock, arg_errmsg, TV_TRANSLATE))) {
       return;
diff --git a/src/nvim/testdir/test_blob.vim b/src/nvim/testdir/test_blob.vim
index c5a217f36f..770b2d16ef 100644
--- a/src/nvim/testdir/test_blob.vim
+++ b/src/nvim/testdir/test_blob.vim
@@ -274,6 +274,7 @@ endfunc
 
 " filter() item in blob
 func Test_blob_filter()
+  call assert_equal(v:_null_blob, filter(v:_null_blob, '0'))
   call assert_equal(0z, filter(0zDEADBEEF, '0'))
   call assert_equal(0zADBEEF, filter(0zDEADBEEF, 'v:val != 0xDE'))
   call assert_equal(0zDEADEF, filter(0zDEADBEEF, 'v:val != 0xBE'))
diff --git a/src/nvim/testdir/test_filter_map.vim b/src/nvim/testdir/test_filter_map.vim
index ebcb6699c6..c75177ea39 100644
--- a/src/nvim/testdir/test_filter_map.vim
+++ b/src/nvim/testdir/test_filter_map.vim
@@ -89,8 +89,10 @@ func Test_map_filter_fails()
   call assert_fails("let l = filter([1, 2, 3], '{}')", 'E728:')
   call assert_fails("let l = filter({'k' : 10}, '{}')", 'E728:')
   call assert_fails("let l = filter([1, 2], {})", 'E731:')
-  call assert_equal(0, map(v:_null_list, '"> " .. v:val'))
-  call assert_equal(0, map(v:_null_dict, '"> " .. v:val'))
+  call assert_equal(v:_null_list, filter(v:_null_list, 0))
+  call assert_equal(v:_null_dict, filter(v:_null_dict, 0))
+  call assert_equal(v:_null_list, map(v:_null_list, '"> " .. v:val'))
+  call assert_equal(v:_null_dict, map(v:_null_dict, '"> " .. v:val'))
 endfunc
 
 func Test_map_and_modify()
diff --git a/test/unit/eval/typval_spec.lua b/test/unit/eval/typval_spec.lua
index 6387f89fe4..34dbf592a5 100644
--- a/test/unit/eval/typval_spec.lua
+++ b/test/unit/eval/typval_spec.lua
@@ -2253,8 +2253,8 @@ describe('typval.c', function()
         local d1 = dict()
         alloc_log:check({a.dict(d1)})
         eq(1, d1.dv_refcount)
-        eq(false, tv_dict_equal(nil, d1))
-        eq(false, tv_dict_equal(d1, nil))
+        eq(true, tv_dict_equal(nil, d1))
+        eq(true, tv_dict_equal(d1, nil))
         eq(true, tv_dict_equal(d1, d1))
         eq(1, d1.dv_refcount)
         alloc_log:check({})
@@ -2721,8 +2721,8 @@ describe('typval.c', function()
         local d1 = lua2typvalt({})
         alloc_log:check({a.dict(d1.vval.v_dict)})
         eq(1, d1.vval.v_dict.dv_refcount)
-        eq(false, tv_equal(nd, d1))
-        eq(false, tv_equal(d1, nd))
+        eq(true, tv_equal(nd, d1))
+        eq(true, tv_equal(d1, nd))
         eq(true, tv_equal(d1, d1))
         eq(1, d1.vval.v_dict.dv_refcount)
         alloc_log:check({})